沂蒙山区不同森林类型凋落物量及其动态特征

Dynamics of litterfall in different forest types in the Yimeng mountainous area

凋落物在森林养分循环中起重要作用,受森林类型、气候带等因素的影响。本文研究了沂蒙山区黑松(Pinus thunbergii Parl.)人工林、栓皮栎(Quercus variabilis Bl.)人工林和天然次生林的凋落物总量和组分的动态特征。天然次生林年凋落物总量(3368 kg/hm2)高于栓皮栎人工林(3256 kg/hm2)高于黑松人工林(3212 kg/hm2),森林类型间差异不显著。3种森林类型的凋落物月总量呈双峰曲线,最大峰值在10—11月,次峰值在4—5月,最小峰值出现时间不同:黑松人工林为12月,另两种森林类型为7月。针叶凋落量和比例、碎屑凋落量表现为黑松人工林高于天然次生林高于栓皮栎人工林,而阔叶凋落量和比例、果凋落量的比例则相反。枝凋落量在森林类型间无显著差异。线性回归分析表明,凋落物总量月动态受最低和最高气温的影响。针叶凋落量受最低气温、最高气温和最大降水量影响;阔叶凋落量受最低气温影响;枝凋落量受降水量、风速和最大降水量影响;果凋落量受气温、风速和降水量影响。结果阐明了暖温带森林类型对凋落物量及组分动态特征的影响,可为其养分循环特征提供数据支撑。

Litter plays an important role as a metabolic product in nutrient cycling and energy transfer in forest ecosystems. Different forest types （ e.g., broad-leaved vs. needle-leaved forests, and natural secondary forests vs. plantations ） are characterized by different litterfall compositions and dynamics, which are associated with different plant community structure, climate zone, and microclimate. The Yimeng mountainous area is located in a warm-temperate zone and contains the earliest plantations in China. In addition to natural secondary forests, the main forest types in this area are plantations of the introduced needle-leaved species Pinus thunbergii Parl. and the native broad-leaved species Quercus variabilis B1. In this study, we analyzed the composition and dynamics of litterfall in these three forest types. Seventeen plots were selected, including six plots in P. thunbergii plantation, six in natural secondary forest, and five in Q. variabilis plantation. In each plot, a 1 m × 1 m sieve was placed 30 cm above the ground for monthly litter collection from May 2015 through April 2017. The collected litter was transferred to the laboratory and sorted into needle leaf, broad leaf, fruit, and other litter, and then dried to a constant weight at 80%. The results showed that natural secondary forests had a higher annual litterfall （ 3368 kg/ hm2） than that of Q. variabilis plantation （3256 kg/hm2） and P. thunbergii plantations （3212 kg/hm2）. However, there was no significant difference in annual litterfall among the three forest types. The monthly dynamics of overall litterfall in the three forest types all had a two-peak curve, with the higher peak occurring during October through November and the lower peak appearing during April through May. However, minimum litterfall occurred at different times in the different forests, namely, October through November in P. thunbergii plantations, and during July in the other two forest types. The curves of needle leaf, broad leaf, and branch litterfall were similar to that of overall litterfall. The branch litterfall changed smoothly, whereas fruit litterfall mainly appeared in August through September. Leaf litter was the largest component of litterfall, accounting for more than 65.9% of the total in all three forest types. The quantity and ratio of needle leaf litterfall, and quantity of other litter in P. thunbergii plantations were higher than those in Q. variabilis plantations, which in turn were higher than those in natural secondary forests. In contrast, the quantity and ratio of broad leaf litterfall showed the opposite trend. There was no significant difference in the quantity of branch litterfall among the forest types. Litterfall components were influenced by different environmental factors. Multiple linear regression analyses showed that monthly litterfall production was significantly negatively correlated with minimum air temperature and significantly positively correlated with maximum air temperature. Needle leaf litter production was significantly influenced by both minimum and maximum air temperature and maximum precipitation; broad leaf litter production was significantly influenced by minimum air temperature; branch litter production was significantly influenced by precipitation, maximum precipitation, and wind speed; and fruit litter production was significantly influenced by air temperature, wind speed, and precipitation. Natural secondary forests had the largest litterfall, which is beneficial in terms of nutrient cycling and soil fertility. Therefore, protecting natural secondary forests from disturbance in the Yimeng mountainous area is important for the enhancement of carbon sequestration and nutrient cycling, and the maintenance of soil fertility.